Microfluidics is considered an important research field, with growing applications potential and promising markets in many technological applications, such as in fluid control devices, medical testing devices (e.g. DNA and protein analysis and drug discovery), etc. Micropumps are one of the most important microfluidic components.
There are generally two types of micropumps, both mainly made by micromachining technology: mechanical pumps (using moving parts such as check valves and oscillating membranes) and non-mechanical pumps (converting electrical energy into kinetic energy in the fluid). Mechanical micropumps are typically of a size in the range of millimetres (many in the range of centimetres, with large flow rates of >10 ml/min). Non-mechanical pumps are typically orders of magnitude smaller, at least in the fluid pumping direction.
While mechanical pumps usually have difficulty in controlling flow rates, especially in low flow-rate applications (e.g., drug delivery), non-mechanical pumps can usually serve as accurate low flow-rate pumps. However, non-mechanical pumps usually have the disadvantages of high-voltage operation (typically hundreds of volts) and low maximum flow rates.
Various kinds of non-mechanical micropumps have been developed in recent years, e.g. electro-dialysis pumps, electro-kinetic pumps, electro-hydrodynamic pumps, magneto-hydrodynamic pumps, phase transfer pumps, electro-wetting pumps and electrochemical pumps.
Electro-dialysis is capable of transporting ionic compounds from one solution to another, for example salts or acids from a dilute solution to a concentrate solution by applying an electric current. Anions and cations pass through anion exchange membranes and cation exchange membranes, respectively. One common use for such a cell is in seawater desalination.
For electro-kinetic pumps, an electrical field is used to pump the fluid, using one of two mechanisms for the electro-kinetic phenomenon: electrophoresis (using an electrical field to drive charged species in a fluid) and electro-osmosis (pumping the fluid through a charges surface of channels in a substrate under an electrical field). Different micropumps have their advantages and specific application fields.
Electro-osmosis has been used to deliver buffer solutions and separating molecules like DNA or proteins. One such pump is described in D. J. Harrison, et al. Proc. of Inter. Conf. On Solid-state Sensors and Actuators Transducers, 1991, p. 792. This was an electro-osmosis pump integrated on silicon and apparently capable of generating a fluid velocity of 100 μm/s using a field strength of 150 V/cm.
Other published prior art includes U.S. Patent Publication No. 6,471,688 B1, issued to Derek J. Harper and Charles F. Milo on 29 Oct. 2002, “Osmotic pump drug delivery systems and methods. The osmotic pump structure described therein uses two semi-permeable membranes of a cellulose acetate composition, one of which is initially covered with an impermeable membrane, such as: titanium, stainless steel, platinum, platinum-iridium, polyethylene, PET or PETG, which is pierced after implantation of the device.
Further, International Patent Application Publication WO 2004/073822 A2, published in the name of Sophion Bioscience A/S on 2 Sep. 2004, “sieve EOF pump” describes an electro-osmotic flow (EOF) pump. A hollow housing has two ports at one end connecting to an internal chamber. The chamber is divided into two compartments by a membrane made from silicon, with one port connecting to each compartment. The surface of the membrane is made hydrophilic by thermal or chemical oxidation, or by deposition of a hydrophilic material such as silicon oxide, glass, silica or alumina. The pore sizes of the membrane are around 0.8 μm in diameter. Electrodes sit on opposing surfaces of the chamber on opposing sides of the membrane to create an electric field to pump an ionic liquid from one compartment to the other.
Additionally, U.S. Patent Publication No. 6,784,007 B1, issued to Tatsuya Iwasaki and Tohru Den on 31 Aug. 2004, “Nano-structures, process for preparing nano-structures and devices”, describes a technique, using anodic oxidation, for preparing porous alumina thin films which contain different sized nanopores. The films are for use in light emitting devices, optical devices and magnetic devices.
It is an aim of the present invention to provide a new micro- or nanopump membrane and micro- or nanopump and a new micro- or nanopump fabrication method.